1. Field of the Invention
The present invention relates to an illumination device and a reflection type liquid crystal device using the same, and more particularly to an illumination device capable of improving an optical efficiency of a light emitted from a light source and a reflection type liquid crystal device using the same.
2. Description of the Related Art
Generally, a voltage is applied to a liquid crystal display device to cause a change in an alignment of liquid crystal. As a result, the liquid crystal cells undergoes a change of optical characteristics such as a birefringence, a rotatory polarization, a dichroism and a light scattering according to the changed alignment of the liquid crystal. Therefore, the liquid crystal display device can display an image according to the changes of the optical characteristics of the liquid crystal cell.
The liquid crystal display is classified into a transmission type liquid crystal display using a backlight and a reflection type liquid crystal display using an external light source, depending on a light source. The transmission type liquid crystal display is widely used, but the use of the backlight increases the power consumption as well as the volume and weight of the liquid crystal display. In order to solve the above drawbacks of the transmission type liquid crystal display having the backlight therein, a reflection type liquid crystal display, which does not use the backlight, has been variously studied and developed.
In addition, the reflection type liquid crystal display is anticipated to replace the transmission type liquid crystal display due to consumer demands on portable information display devices. Computer terminals using such a reflection type liquid crystal display to which a white-and-black TN mode or a white-and-black STN mode is applied, are commercially available and research and development for a color reflection type liquid crystal display is currently underway.
The development of the color reflection type liquid crystal display is one of the important subjects targeted in IMT-2000 (International Mobile Telecommunications-2000), which is actively studied and developed as a next generation mobile telecommunication. In this regard, extensive research for lighter, slimmer and compact-sized structures is currently underway.
FIG. 1 is a schematic plan view showing an illumination device used in a conventional reflection type liquid crystal display.
Referring to FIG. 1, the illumination device 30 used in the conventional reflection type liquid crystal display includes a light source section 10 and a light guiding section 20, which is provided at a side of the light source section 20 and guides the light from the light source section 10 to a liquid crystal display panel (not shown).
The light source section 10 includes a plurality of light sources 11a and 11b for emitting the light and a first light guiding plate 12, which is provided at a side of the light sources 11a and 11b for guiding the light towards the light guiding section 20. The light sources 11a and 11b include a light emitting diode (LED) in the form of a point-shaped light source. The light sources 11a and 11b are respectively installed at both ends 12a and 12b of the first light guiding plate 12, so that the light emitted from the light sources 11a and 11b are incident into both ends 12a and 12b of the first light guiding plate 12.
The first light guiding plate 12 has a hexahedron bar structure. The light guiding section 20 is arranged at a first side 12c of the first guiding plate 12 and patterns 12e are formed at a second side 12d of the first guiding plate 12 opposite the first side 12c. The light, which is incident into both ends 12a and 12b of the first guiding plate 12, is reflected by the patterns 12e formed at the second side 12d of the first guiding plate 12 and incident into the light guiding section 20 through the first side 12c of the first guiding plate 12.
The light guiding section 20 has a hexahedron plate structure. The light guiding section 20 is arranged above the liquid crystal display panel and guides the light incident from the light source section 10 towards the liquid crystal display panel.
However, in order to make a large screen for the reflection type liquid crystal display, it is required to increase the amount of the light emitted from the light source section 10 to obtain a desired brightness. In order to increase the amount of the light emitted from the light source section 10, it is necessary to increase the number of light sources 11a and 11b installed at both ends 12a and 12b of the first light guiding plate 12, so the width of the first light guiding plate 12 is also increased.
FIG. 2 is a plan view showing the conventional light source section with increased number of light sources.
Referring to FIG. 2, the light source section 10 includes a plurality of light sources 13a to 13h which are arranged at both ends 12a and 12b of the first light guiding plate 12. In FIG. 2, four light sources are arranged at each end of the first light guiding plate 12. The widths of both ends 12a and 12b of the first light guiding plate 12 are enlarged corresponding to the increased number of the light sources 13a to 13h. 
Therefore, since the number of the light sources 13a to 13h arranged at both ends 12a and 12b of the first light guiding plate 12 is increased by four times as compared with the number of the light sources 11a and 11b shown in FIG. 1, the brightness thereof has to be correspondingly improved.
However, as shown in FIG. 2, when the light sources 13a to 13h are arranged at both ends 12a and 12b of the first light guiding plate 12, the light sources 13a and 13e are relatively adjacent to the patterns 12e, but the light sources 13d and 13h are relatively remote from the patterns 12e. The light generated from the light sources 13d and 13h remote from the patterns 12e of the first light guiding plate 12 rarely arrives at the patterns 12e of the first light guiding plate 12 as compared with the light generated from the light sources 13a and 13e adjacent to the patterns 12e. 
Accordingly, even though the number of light sources 13a to 13h arranged at both ends 12a and 12b of the first light guiding plate 12 increases, the brightness of the reflection type liquid crystal display cannot be sufficiently improved in proportion to the number of light sources.
The present invention solves the aforementioned problems, and provides an illumination device capable of improving an optical efficiency of a light emitted from a light source section.
Further, the present invention provides a liquid crystal display device having an illumination device capable of improving an optical efficiency of a light emitted from a light source section.
In one aspect of the invention, there is provided an illumination device including a light generator means for generating a light, a first light guiding plate including a first portion through which the light is incident and a second portion from which the light is emitted, and a second light guiding plate including opposite first and second side portions, at least one of which is adjacent to the light generator, a light projecting portion adjacent to the first portion of the first light guiding plate and a light reflecting portion having a distance from the light projecting portion. At least one light source is disposed adjacent to at least one of first and second side portions of the second light guiding plate for providing the light into the second light guiding plate. The distance between the light projecting portion of the second light guiding plate and the light reflecting portion becomes narrow as a number of light flex of the light emitted from the light generator decreases.
According to one embodiment of the present invention, at least one light source may be a point-shaped light source.
The light reflecting portion of the second light guiding plate includes a concave section. The concave section may have a V-shape inclined from opposite side ends of the light reflecting portion adjacent to the first and second side portions.
The concave section has a bottom portion, and a position of the bottom portion is defined by a following equation: x:y=w1:w2, wherein, x is a linear distance from the first side portion to the bottom portion, y is a linear distance from the second side portion to the bottom portion, x+y is a linear distance from the first side portion to the second side portion, w1 is a width of the first side portion, and w2 is a width of the second side portion. A value of x may be substantially equal to a value of y.
The number of the light source disposed adjacent to the first side portion is the same as or different from the number of the light source disposed adjacent to the second side portion.
The widths of the first and second side portions are defined by a following equation; w1:w2=n1:n2, wherein w1 is the width of the first side portion, and w2 is the width of the second side portion, n1 is the number of the light source disposed adjacent to the first side portion, and n2 is the number of the light source disposed at the second side portion.
A linear distance between of the bottom portion of the light reflecting portion and the light projecting portion is variable with respect to the widths of the first and second side portions so as to be smaller than a smaller width of the widths of the first and second side portions.
A plurality of groove patterns is formed at the concave section of the second light guiding plate.
The second light guiding plate includes a light scattering member, which uniformly diffuses the light incident through the first and second side portion and uniformly distributes a light flux of the light projected through the light projecting portion.
In another aspect, there is provided a reflection type light crystal display device comprising a liquid crystal display panel for displaying an image and an illumination device disposed in a front of the liquid crystal display panel. The illumination device includes light generator means for generating a light, a first light guiding plate including a first portion through which the light is incident and a second portion from which the light is emitted, and a second light guiding plate including opposite first and second side portions, at least one of which is adjacent to the light generator, a light projecting portion adjacent to the first portion of the first light guiding plate and a light reflecting portion having a distance from the light projecting portion. The distance between the light projecting portion of the second light guiding plate and the light reflecting portion becomes narrow as an amount of light flux of the light emitted from the light generator decreases.
Therefore, even when the number of the light sources disposed at a side of the second light guiding plate is increased, the light efficiency of the plurality of light sources can be improved by increasing the probability of variation in optical routes for the light emitted from the light sources and by allowing the light to arrive at the concave section.